1. Technical Field
The present invention relates to gas barrier films and methods for producing the gas barrier films. More specifically, the present invention relates to a gas barrier film used in a package generally for an electronic device or the like, or in an organic electroluminescence (EL) element, a solar cell element, a liquid crystal display element, or the like and to a method for producing the gas barrier film.
2. Description of Related Arts
Conventionally, gas barrier films formed by laminating a plurality of layers containing thin films of metallic oxides such as aluminum oxide, magnesium oxide, and silicon oxide on plastic substrate and film surfaces have been widely used for packaging articles needing to be shielded against various gases, such as moisture vapor and oxygen, and for packaging applications for preventing change in quality of food products, industrial products, pharmaceutical products, and the like.
In addition to packaging applications, they have been used in solar cell elements, organic electroluminescence (EL) elements, liquid crystal display elements, and the like.
As a method for forming such a gas barrier film, there has been known a gas phase method such as a chemical deposition method (plasma CVD method: Chemical Vapor Deposition) by which a film is formed on a substrate while oxidizing an organosilicon compound represented by tetraethoxysilane (TEOS) by oxygen plasma under reduced pressure or a physical deposition method (vacuum deposition method or sputtering method) by which metallic Si is evaporated to deposit a gas barrier layer on a substrate using a semiconductor laser in the presence of oxygen.
These methods have been preferably used for forming metal oxide thin films including SiO2 since a thin film with accurate composition can be formed on a substrate; however, they have had significantly poor productivity in view of the fact that reduction in pressure and atmospheric opening in a film production apparatus need time due to the formation of the films under reduced pressure and in view of the fact that decrease in film production rate is needed for obtaining dense film quality providing a good gas barrier property since poor film quality with many defects is caused by increasing a film production rate.
An attempt to form a silicon oxide thin film by coating a silicon-containing compound to modify the coating film has been made for the purpose of improving productivity to solve such problems, and the examination has been also carried out for gas barrier films.
There has been generally known a technology to form a silicon oxide film which can be produced in a solution process by a method called a sol-gel process with an alkoxide compound as a source material. In the sol-gel process, heating at high temperature is generally necessary and a large volume shrinkage farther occurs in the process of a dehydrative condensation reaction to generate a large number of defects in the film.
Although there has been known a procedure of mixing a source material solution with organic substances which are not directly involved in formation of oxides to prevent this problem, a barrier property is deteriorated to cause an insufficient barrier property in view of the whole film due to the remaining of these organic substances in the film.
Based on them, it has been difficult to use an oxide film produced in the sol-gel process as a protection film for a flexible electronic device directly.
As another method, there has been proposed formation of a silicon oxide film using, as a source material, a silazane compound having a silazane structure (Si—N) as a basic structure.
It has been known that, since the reaction in this case is not dehydrative condensation polymerization but a direct substitution reaction from nitrogen to oxygen, a mass yield before and after the reaction is as high as 80% to 100% and a dense film with a few defects in the film due to volume shrinkage is obtained.
However, the formation of the silicon oxide film by the substitution reaction of the silazane compound requires a high temperature of 450° C. or more and it was not able to be adapted to a flexible substrate such as a plastic.
As means for solving such a problem, there has been proposed a method for forming a silicon oxide film by irradiating a coating film formed by coating from a solution containing a silazane compound and a compound releasing amines, with vacuum-ultraviolet light (see Patent Literature 1).
The silicon oxide film can be formed at a comparatively low temperature by making an oxidation reaction due to active oxygen or ozone proceed while directly cutting an atomic bond by the action only of a photon, referred to as a light quantum process, by using larger light energy with 100 to 200 nm, referred to as vacuum-ultraviolet light (hereinafter also described as “VUV” or “VUV light”), than interatomic bonding force in a silazane compound.
Further, it is necessary to enable continuous production industrially in so-called roll-to-roll from the viewpoint of the production of a gas barrier film.
In addition, there have been known methods of transporting a film at a rate of around 1 m/min or 10 m/min and irradiating a silazane compound coating film with an excimer lamp to produce a gas barrier film, as methods for the production in roll-to-roll (see Patent Literature 2 and Hon Patent Literature 1).
However, these methods also have had such problems that productivity is insufficient and the barrier performance of the produced gas barrier film is quite insufficient for a gas barrier layer for an organic photoelectric conversion element or the like.
On the other hand, there has been, also examined that a composite-type gas barrier layer in which a gas barrier layer formed by coating is laminated on a gas barrier layer formed by a gas phase method such as CVD or sputtering. It has been examined for the purpose of repairing the defect of the gas barrier layer, formed by the gas phase method, by the gas barrier layer formed by the coating, and has the possibility of obtaining a good gas barrier property while increasing the productivity of the gas barrier layer formed by the gas phase method.
For example, Patent Literature 3 discloses a method of further improving barrier performance by laminating and coating polysilazane on a gas barrier layer formed on a resin base by a vacuum plasma CVD method and by repairing the gas barrier layer by heat treatment. However, the gas barrier layer obtained by this method has been insufficient as a gas barrier layer for an organic photoelectric conversion element or the like and has been significantly poor in productivity since the heat treatment of polysilazane at 160° C. for as long as 1 hour is needed.
As described above, there has been demanded a method for producing a gas barrier film enabling compatibility between a very high barrier property required by an organic photoelectric conversion element or the like and productivity.